Micro-finishing is a surface finishing process wherein an abrasive is brought to bear against a workpiece having a rough outer surface. By improving the surface finish, less friction will be produced between the workpiece and any contact surface thereby extending the life of the workpiece. Non-metallic products, such as wood, glass, rubber and plastic can also be micro-finished.
How a workpiece is micro-finished depends on its shape and size. Viewing FIGS. 1-4 herein, "centerless" or "center" operations dictate how a workpiece is held in place during the finishing process. Center operations are appropriate when the workpiece is large enough in diameter and length to be supported at each end for rotation, such as with a chuck on a lathe. However, when the diameter or the length of a workpiece is too small to be supported by a lathe, centerless operations may be used by placing the workpiece, for example, between two rotating rollers, as seen in FIGS. 2 and 4.
In addition, a workpiece contacts the abrasive either through "plunge" or "transverse" operations. A workpiece is subject to finishing by plunge operations when the workpiece's length is less than or equal to the width of the available abrasives. The entire length of the workpiece is constantly in contact with the abrasive. Transverse finishing is used when the workpiece is longer than the width of any available abrasives. In which case the abrasive must travel along the longitudinal axis of the rotating workpiece as it micro-finishes.
It is therefore well known in the art that the shape and size of the metal product will determine which one of the various micro-finishing machines would produce the best finish: 1) plunge-center; 2) plunge-centerless; 3) transverse-center; or 4) transverse-centerless.
For purpose of this invention, it is important to expand upon the typical transverse centerless micro-finishing machine known in the art. When cylindrical metal workpieces are micro-finished using the transverse centerless micro-finishing type machine, the workpieces are placed between two rollers as seen in FIG. 4. The rollers are located beneath the abrasive and are offset at an angle for feeding the part through the micro-finishing apparatus. Hence, this process is also often referred to as "through-feed centerless" micro-finishing. The rollers rotate in the same direction very quickly, thereby rotating the part along the abrasive. Problems occur when workpieces are very small, such as those having diameters less than 3/8 of an inch or 8 millimeters. Particularly, transverse centerless cylindrical workpieces are difficult to micro-finish, if not impossible for small parts, because the abrasive cannot reach the small workpiece positioned between the rollers. This is due to the large difference in diameter between the rollers and the workpiece. More specifically, the diameter of the workpiece is so small that the abrasive contacts the rollers and never reaches the workpiece positioned therebetween. Also, conventional methods of holding the workpiece during finishing, such as using a lathe, cannot be used because the workpieces are just too small to be held by the chuck.
Art in the field may also be directed to grinding machines, as opposed to micro-finishing machines. Typical grinding machines are shown in FIGS. 5 and 6. These machines are comprised of a regulating mechanism, an abrasive and a means of supporting the workpiece at a fixed location. However, none of the grinding machines in the art can be used to solve the problem of micro-finishing miniature cylindrical workpieces. Problems exist in traditional grinding processes because of the abrasive used. In traditional grinding processes, the abrasive is a wheel or continuous belt that travels very fast, constantly being reused. As a result, the finish varies as the abrasive wears. Also, the contact surface of the abrasive is short if a plurality of workpieces are continuously fed through typical grinding machines. The preferred apparatus should repeatably produce consistent micro-finishing results to the entire outside surface of very small centerless workpieces.
In summation, there is nothing currently in the art capable of micro-finishing small workpieces. The purpose of this invention is to provide an apparatus that can micro-finish the outer surface of very small cylindrical workpieces with repeatability and consistency.